Fishpond
Encyclopedia
Fishpond was the code name
given to an extension to the British H2S
airborne radar system fitted to Royal Air Force
(RAF) Avro Lancaster
and Handley Page Halifax
heavy bomber
s during World War II
. It was designed to give early warning of German
night fighters approaching in the hemisphere
below the carrying aircraft out to a range of 30 miles (48.2 km).
The H2S radar was a navigation
al aid designed to give a map
-like display of the ground below the aircraft. The display, known as a Plan Position Indicator
(PPI), used a scanning electron beam in a Cathode Ray Tube
which scanned from the centre of the display to the edge in a direction corresponding to the direction in which the radar's scanning head was pointing. In order that the centre of the display represented the ground immediately beneath the aircraft, the scan had to be delayed to allow for the transmitted radar pulses to travel from the aircraft to the ground and back again. This delay was derived from a simple radio altimeter.
It was realised that during this undisplayed time echoe
s would be returning from any other aircraft within the vicinity of the bomber. Accordingly a second display was installed in the radio
operator's position which displayed the image suppressed from the navigator's display. This display showed the relatively stationary blips
from the bomber formation and, most importantly, the rapidly moving returns from the German night fighters.
Code name
A code name or cryptonym is a word or name used clandestinely to refer to another name or word. Code names are often used for military purposes, or in espionage...
given to an extension to the British H2S
H2S radar
H2S was the first airborne, ground scanning radar system. It was developed in Britain in World War II for the Royal Air Force and was used in various RAF bomber aircraft from 1943 to the 1990s. It was designed to identify targets on the ground for night and all-weather bombing...
airborne radar system fitted to Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
(RAF) Avro Lancaster
Avro Lancaster
The Avro Lancaster is a British four-engined Second World War heavy bomber made initially by Avro for the Royal Air Force . It first saw active service in 1942, and together with the Handley Page Halifax it was one of the main heavy bombers of the RAF, the RCAF, and squadrons from other...
and Handley Page Halifax
Handley Page Halifax
The Handley Page Halifax was one of the British front-line, four-engined heavy bombers of the Royal Air Force during the Second World War. A contemporary of the famous Avro Lancaster, the Halifax remained in service until the end of the war, performing a variety of duties in addition to bombing...
heavy bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
s during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. It was designed to give early warning of German
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
night fighters approaching in the hemisphere
Sphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
below the carrying aircraft out to a range of 30 miles (48.2 km).
The H2S radar was a navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
al aid designed to give a map
Map
A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....
-like display of the ground below the aircraft. The display, known as a Plan Position Indicator
Plan position indicator
The plan position indicator , is the most common type of radar display. The radar antenna is usually represented in the center of the display, so the distance from it and height above ground can be drawn as concentric circles...
(PPI), used a scanning electron beam in a Cathode Ray Tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
which scanned from the centre of the display to the edge in a direction corresponding to the direction in which the radar's scanning head was pointing. In order that the centre of the display represented the ground immediately beneath the aircraft, the scan had to be delayed to allow for the transmitted radar pulses to travel from the aircraft to the ground and back again. This delay was derived from a simple radio altimeter.
It was realised that during this undisplayed time echoe
Echo (phenomenon)
In audio signal processing and acoustics, an echo is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single...
s would be returning from any other aircraft within the vicinity of the bomber. Accordingly a second display was installed in the radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
operator's position which displayed the image suppressed from the navigator's display. This display showed the relatively stationary blips
Radar display
Modern radar systems typically use some sort of raster scan display to produce a map-like image. In the past, notably during the early days of radar development, such displays were difficult to produce for a number of reasons. Several different display types were developed during this...
from the bomber formation and, most importantly, the rapidly moving returns from the German night fighters.